Piezoelectric sensor, touch panel, touch input device, and display device

Abstract

A piezoelectric sensor includes: a piezoelectric sheet which is stretched in a uniaxial direction; an electrode which detects electric charges generated in the piezoelectric sheet; and an optical compensation layer which includes a slow axis stacked on at least one side of the piezoelectric sheet and intersects the uniaxial direction, and optically compensates for a phase difference produced when the piezoelectric sheet is stretched in the uniaxial direction.

The invention claimed is: 
     
       1. A piezoelectric sensor comprising:
 a piezoelectric sheet which is stretched in a uniaxial direction; 
 an electrode which detects an electric charge generated in the piezoelectric sheet; and 
 a non-piezoelectric optical compensation layer which includes a slow axis disposed on at least one side of the piezoelectric sheet and intersects the uniaxial direction, and optically compensates for a phase difference produced when the piezoelectric sheet is stretched in the uniaxial direction. 
 
     
     
       2. The piezoelectric sensor according to  claim 1 , wherein a retardation value of the optical compensation layer is within a range of 40% to −30% of a retardation value of the piezoelectric sheet. 
     
     
       3. The piezoelectric sensor according to  claim 1 , wherein a retardation value of the optical compensation layer is within a range of ±30% of a retardation value of the piezoelectric sheet. 
     
     
       4. The piezoelectric sensor according to  claim 1 , wherein the slow axis of the optical compensation layer is orthogonal to the uniaxial direction. 
     
     
       5. The piezoelectric sensor according to  claim 2 , wherein the slow axis of the optical compensation layer is orthogonal to the uniaxial direction. 
     
     
       6. The piezoelectric sensor according to  claim 3 , wherein the slow axis of the optical compensation layer is orthogonal to the uniaxial direction. 
     
     
       7. The piezoelectric sensor according to  claim 1 , wherein the piezoelectric sheet contains polylactic acid. 
     
     
       8. The piezoelectric sensor according to  claim 1 , wherein:
 the electrode is formed on an electrode film; and 
 the electrode film is the optical compensation layer. 
 
     
     
       9. The piezoelectric sensor according to  claim 2 , wherein:
 the electrode is formed on an electrode film; and 
 the electrode film is the optical compensation layer. 
 
     
     
       10. The piezoelectric sensor according to  claim 3 , wherein:
 the electrode is formed on an electrode film; and 
 the electrode film is the optical compensation layer. 
 
     
     
       11. The piezoelectric sensor according to  claim 4 , wherein:
 the electrode is formed on an electrode film; and 
 the electrode film is the optical compensation layer. 
 
     
     
       12. A touch panel comprising:
 the piezoelectric sensor according to  claim 1 ; and 
 an operation surface. 
 
     
     
       13. A touch input device, comprising:
 the touch panel according to  claim 12 ; and 
 a detector which detects the charge generated in the piezoelectric sensor by a pressing operation on the operation surface. 
 
     
     
       14. A display device, comprising:
 the touch panel according to  claim 12 ; and 
 a display panel, 
 wherein the display panel forms a display image by controlling light emitted toward the operation surface, and includes a top polarizing plate which is disposed closer to the operation surface than the display panel. 
 
     
     
       15. The display device according to  claim 14 , wherein
 a second optical compensation layer is disposed on a side opposite to the optical compensation layer so as to sandwich the piezoelectric film, and 
 the second optical compensation layer includes a slow axis which forms 45 degrees with respect to a polarization direction of the top polarizing plate. 
 
     
     
       16. A piezoelectric sensor comprising:
 a piezoelectric sheet which is stretched in a uniaxial direction; 
 an electrode which detects an electric charge generated in the piezoelectric sheet; and 
 a non-piezoelectric optical compensation layer which includes a slow axis disposed on at least one side of the piezoelectric sheet and intersects the uniaxial direction, and has a retardation value within ±30% of a retardation value of the piezoelectric sheet.